The evolution of most quantum systems is modeled by differential equation in the complex space. However, in general, the equations are numerically solved using integrators with real coefficients. To consider complex coefficients usually does not make the schemes computationally more costly and can provide more accurate results. In this talk, we explore the applicability of splitting methods involving complex coefficients to solve numerically the time-dependent Schrödinger equation. There are pros (high accuracy and not to increase the cost) and cons (instability and loose of qualitative properties) when using complex coefficients. However, there is a class of methods with complex coefficients with a particular symmetry that keep most pros while avoid most cons. This class of integrators are stable and are conjugate to unitary methods for sufficiently small step sizes. These are promising methods that we will explore: we build new methods and we analyse their performance on several examples. This is joint work with Joakim Bernier, Fernando Casas and Alejandro Escorihuela.

• Thematic program: Quantum Mechanics (2023/2024)
• Event: Workshop on "Complex operator splitting methods for Ginzburg-Landau equations and related problems" (2024)

In this talk I will provide a short introduction to a class of operator splitting methods with complex coefficients which possess a special symmetry, the so-called symmetric-conjugate methods, and analyze their application for the time integration of linear evolution problems. Including complex coefficients with non-negative real parts permits the design of favorable high-order schemes that remain stable in the context of parabolic problems. This sets aside the second-order barrier for standard splitting methods with real coefficients as well as the fourth-order barrier for modified splitting methods involving double commutators. Relevant applications include nonreversible systems and ground state computations for Schr{\"o}dinger equations based on the imaginary time propagation method.

• Thematic program: Quantum Mechanics (2023/2024)
• Event: Workshop on "Complex operator splitting methods for Ginzburg-Landau equations and related problems" (2024)